{Sub-order 1. Chilostomata.[15] {Order I. Gymnolæmata.[16] { Orifice of cell with a { Lophophore and tentacular { horny lid. { crown circular. { { Without a lobe over {Sub-order 2. Ctenostomata.[17] { the mouth. { Orifice of cell closed { { by a membranous Group I. Ectoprocta.[14] { { comb-like frill. Vent opens outside {Order II. Phylactolæmata.[18] { Always fleshy or the circle of tentacles.{ Lophophore and tentacular { horny. { crown horse-shoe { { shaped. With {Sub-order 3. Cyclostomata.[19] { lobe over the mouth. { Without lid or frill; { Fresh water forms. { orifice of cell usually { circular; cells { always calcareous. Group II. Entoprocta.[20] Vent opens inside circle of tentacles. _Sub-order 1._—CHILOSTOMATA. [Sidenote: Cases A and B 1.] The Chilostomata, which contain many more species than all the other groups put together, are divided into three sections:—_A._ Cellularina, in which the cells are more or less boat-shaped or cornucopia-shaped, and joined together to form flexible branching colonies; _B._ Flustrina, in which the cells are typically shaped like oblong boxes with membranous front walls; and _C._ Escharina, in which the whole front wall is calcified. [Sidenote: Case A 1.] [Illustration: Fig. 6. A, _Bugula turbinata_, natural size, B, portion × 50. _a_, avicularia; _m_, mouth; _o_, ovicell. [‘The Cambridge Natural History.’] ] _Section A._ CELLULARINA.—_Bugula turbinata_, or the Bird’s-head Coralline (Fig. 6) grows attached to rocks near low water mark in the form of spiral tufts about two inches in height, composed of narrow flat branches in which the cells are arranged from two to six abreast and all facing upwards. Each cell is boat-shaped and with nearly the whole front surface membranous; the globular bodies at the head of certain cells are the ovicells. Attached to the outer edge of each cell is a remarkable object resembling a bird’s head, and hence termed avicularium, seated on a short stalk. The head and beak contain powerful muscles for opening and shutting a horny lid or mandible hinged on below. In life, the avicularium sways to and fro on its stalk, with the lower “jaw” continually snapping up and down in the most ludicrous fashion. The beak is capable of seizing and holding quite large objects.